When Jon Armond was about six years old, he was traumatized by something he saw on Sesame Street. It happened sometime in the mid-1970s: He was watching the show in his living room, surrounded by bad wallpaper and shag carpeting, and in between segments with Mr. Hooper and Cookie Monster, a bizarre cartoon suddenly appeared. Jon remembers it starting with a little girl lying in her bedroom. A crack in her wall morphs into the shapes of different animals: a camel, a hen, a monkey. She then encounters “the crack monster,” a splintery crack that resembles a snarling face.

“It was terrifying that somebody’s wall came to life,” recalls Armond, a voiceover actor in Los Angeles. “And I remember in my own bedroom I had wallpaper, but some of that wallpaper was a little old, and it was coming off in some spots, and I just knew that one of these days, something was going to be behind there and it was going to get me.”

Armond was haunted by the video for decades. He mentioned it to other Gen X’ers who’d been brought up watching Sesame Street, but no one else seemed to remember it. Did the the video even exist, or was his memory just playing tricks on him? Finally, after decades of looking, in the earlier days of the internet, he found Jennifer Bourne, a cartoonist who also grew up fearing the crack monster. She began poking around on Muppet-themed message boards and Snopes, and, little by little, an odd congregation of people started to form online, a virtual support group for people who were terrorized by the clip. People wrote in from California all the way to the United Kingdom.

“This is so strange I thought I was alone in how this little cartoon freaked me out.”

“I had a horrible reoccurring nightmares based on it the whole time.”

“Seriously I’ve been looking for this clip forever because it scared me so much as a kid.”

“I am so very relieved to see that it either really existed or that we all have some kind of mass psychosis.”

”If anybody finds it, post post post!”

But they still couldn’t find the video itself, and Children’s Television Workshop, which produces Sesame Street, was of no help at the time. Still, after making inquiries, Armond eventually got a fax from an unknown, untraceable number promising to send him the copy of “Cracks,” as long as he agreed never to screen it in public, post it online, or send it to anyone else. Armond signed the agreement, and six months passed before he found a manila envelope in his mailbox with a DVD inside. The note read: “We trust this completes your search.” There was no return address, no postmark, and no postage.

He showed the tape to Bourne in 2009, and he was inundated by requests to make it public. One of the requests came all the way from Australia, where Daniel Wilson, the founder of the Lost Media Wiki, a website dedicated to tracking down elusive material, had been trying to get a copy for years. Armond declined to share his version. “I don’t know how long the statute of limitations is on that thing I signed, but I don’t want to take any chances,” he said.

Then, without warning, in December 2013, Wilson received an anonymous email. No message, just an attachment. It was “Cracks.”

In the latest podcast from Studio 360(which along with being a public-radio show is a Slate podcast), producer Sam Kim tells the story of the mystery of the “Cracks” video and uncovers new details about it that even Armond and other online sleuths hadn’t discovered. This includes tracking down the previously unknown woman who voiced the little girl—who turns out to be a renowned experimental rock musician.